The present invention is an engineered wood-based product that is highly effective as a long lasting mulch for prevention of soil erosion.
Siltation of spawning streams from road construction and logging has been a major cause of the decrease of salmon runs in the streams of both western and northeastern United States. Considerable emphasis is now being placed on prevention of erosion from construction projects of almost any size. Logging clear cuts have been greatly restricted in size. Road construction is now carefully engineered to control run-off from rain. Even the smallest construction jobs must now use some sort of erosion control to prevent ultimate soil transport from disturbed land into the closest stream.
In order to prevent erosion it is common practice to apply organic mulches to disturbed surfaces. These maybe of fugitive nature; i.e., those that quickly decay, or they may be more permanent, lasting one or more years. Wheat straw is one of the former type that is widely used while wood chips are typical of the more durable mulches. Short duration mulches are often applied to hold grass seed in place until it germinates and becomes established. These are often based on wood fiber and are usually applied using so-called hydroseeding.
There are both advantages and disadvantages to each of the above types. Straw often carries seeds that may introduce undesirable plant species into an area. As noted, it is short lived and it tends to be displaced by rain runoff when strewn on steeper slopes. It may also carry pesticide residues that can contaminate nearby streams. Wood chips tend to be readily carried away by slope wash. Other types, such as burlap or similar materials, are expensive both in initial and application costs.
Wood chips or comminuted wood have been proposed in the past as a mulch material. Corbett, in U.S. Pat. No. 5,301,460, describes a wood based mulch produced by passing whole wood through a swing hammer mill. This is the type commonly used for reducing waste wood for use as fuel, a product typically called xe2x80x9chog fuelxe2x80x9d. The mulch is said to have xe2x80x9c . . . a shredded fine portion, a bulky portion, and a stringy binding portionxe2x80x9d. The stringy binder appears to be key to distinguishing it from other types of wood based materials since it is said to remain on top and form the mulch into a mat after the fines have sunk to the bottom.
Buchanan et al., in a paper presented at a July 2000 meeting of the American Society of Agricultural Engineers in Milwaukee, Wis. (Paper 002060), explored the use of various sizes of wood chips on a relatively steep slope of an erodible soil. They found that small chips were not very effective but that a mixture of chip sizes gave better protection than either small or large chips.
Pannkuk et al., in Paper No. 005018 presented at the same meeting, found that Douglas-fir and ponderosa pine needles applied at a rate of 70% cover on a simulated 40% slope were effective at reducing soil transport. The Douglas-fir needles were somewhat more effective. This was believed to be due to their somewhat greater soil contact than the longer pine needles. Mulches of this type would generally be of relatively short effectiveness due to rapid decay. These authors discuss mechanics of mulches in reducing soil wash including the effects of raindrop impact and surface water transport.
By and large, mulch materials have been selected because they were inexpensive and readily available. Little thought seems to have been given to the possibility of designing a mulch material based on sound engineering, hydraulic, and biological principals. The present invention is such a material.
The present invention is a mulch material engineered to provide superior soil protection when made and used in accordance with the procedures to be outlined. It is manufactured from wood or wood-like materials and has the properties of relatively long persistence and freedom from seeds that might introduce environmentally undesirable species. The terms xe2x80x9cwood-like materialsxe2x80x9d or xe2x80x9cwood based materialsxe2x80x9d may include products such as heavy paperboard, old corrugated containers, and similar products, and the term xe2x80x9cwoodxe2x80x9d should be read broadly so as to include these. Wood itself is a preferred material. The composition of the product may be varied to meet the particular requirements of climate, slope, or soil type.
Unlike other wood-based mulches, such as fiber, chips, or hog fuel types, the present mulch material is formed from a mixture of at least two components of geometrically regular elements. These components will differ from each other in configuration by length, width or geometric shape. Mixtures of different shapes are acceptable and may, in some cases, be preferred. The individual elements will have a minimum length of about 50 mm and a maximum length of about 300 mm. They are preferably in the range of about 50-250 mm long. The width should be within the range of about 3-30 mm, preferably about 3-16 mm. Thickness of the individual elements should fall within the range of about 2.5-7.5 mm, preferably about 3-6.5 mm. Regardless of the geometric shape or mixture of shapes, about 5-50% of the elements should be longer than the others, preferably by at least 25-50 mm. Greater differences in length are possible.
One preferred geometric shape of the elements is an elongated rectangular parallelepiped. These will be generally of approximately square cross section and will somewhat resemble straws or chop sticks. Other shapes, best described as seen in plan view, are rectangles, elongated diamonds, flattened polygons, or somewhat curvilinear boat shaped pieces.
The product may be made from round wood by sawing, peeling, slicing, shearing, or extrusion through a die. A preferred raw material is lower grades of rotary cut veneer. This may be scrap pieces, often called xe2x80x9cfishtailsxe2x80x9d, that are trimmed from veneer sheets to remove defects or taper during plywood or laminated veneer lumber manufacture. Wood species is not critical. Douglas-fir and the southern pines, e.g. loblolly pine, are more readily available in veneer form than other tree species and have been found to serve very well. Aspen, alder, birch, and similar hardwood species are equally usable. These may be shorter lived yet may better promote soil formation.
The product has been used effectively on a variety of soil types, both in laboratory and field tests. A 70% coverage has been found to provide virtually 100% retention in test plots, even on steep slopes. The product can be readily tailored to match soil or slope type. As one example, the longer fraction should be increased on steeper slopes. Areas where intense rainstorms are normal may have a greater percentage of wider elements to minimize soil displacement from the impact of raindrops. For elements of equal surface area, wider elements will have less upslope edge to hold soil particles than will longer, narrower ones. The longer straw-like elements are important, not only for soil retention, but they link all of the elements to assure the integrity and retention of the mulch during storms.
In contrast to other mulch materials, by forming the mulch of the present invention from engineered predetermined geometric shapes its performance is dependable and reproducible in any given environment.
It is an object of the present invention to provide a mulch material that has been designed using sound engineering principles to effect maximum soil retention over time.
It is another object to provide a mulch material that may be tailored in composition to give optimum performance on a variety of soil types and slopes.
It is a further object to provide a mulch material that may be formed from inexpensive grades or scrap pieces of wood veneers.
It is also an object to provide a method of using a wood-based mulch to effect maximum soil retention in a variety of environments.